Cystic Fibrosis (CF) is a common inherited life-threatening disease affecting approximately 20,000 individuals in the United States. The defective gene in CF encodes for a protein termed the cystic fibrosis transmembrane regulator (CFTR). CFTR function results in ofrmation of thick adherent viscous mucus, which causes luminal obstruction in the lungs and eventual organ damage. The development of mucus stasis contributes to impaired bacterial clearance and creates a microenvironment conducive to bacterial proliferation. This provides stimulus to recruitment and activation of polymorphonuclear leuckocytes (PMNs) in the airways. The PMNs release massive quantities of of toxic substances onto the epithelial surface, which has dual effect of damaging the airway and recruiting additional PMNs. The most important PMN derived substance is felt to be neutrophil elastase. DMP 777 is a compound that inhibits neutrophil elastase within the intra and extracellularly. Phase 1 studies have indicated that the drug is well tolerated in normal patients. The goal of this study is to administer various doses of DMP777 to CF patients over the age of 18, and measure the pharmacokinetic and pharmacodynamic characteristics using timed serum samples. The drug will be administered for 9 days and patients will be monitored for signs of toxicity.